I subbed in a fourth grade classroom today.
During math, the kids were working on multiplying whole numbers by fractions. Apparently this is no longer taught the same way I learned it, and the kids made sure I realized this.
Later, during Social Studies, we were reading about the three branches of government, and then different types of governments. Having started the lesson by telling them that Social Studies was "my area," I encouraged them to ask me any questions they might have on the material, because odds are I could answer them. The questions started out about dictatorships, and ended up being very specific questions about Hitler and WWII.
Also, at some point during the day, a girl asked me if you can patent a religion.